Metabolism of glucose: Glycolysis

Glycolysis is a metabolic pathway converting glucose to pyruvate. It takes place in a cellular compartment called the cytoplasm. This pathway is highly regulated and the muscle can, within a fraction of seconds, increase its activity hundred-fold.

Its yield in terms of ATP residues is rather small (on the average 2 molecules of ATP per molecule of glucose) and glycogen, the polymer of glucose stored in our cells, is rapidly exhausted.

This metabolic pathway also releases protons and the drop of intracellular pH provoked by this increase of protons (acidosis) blocks phosphofructokinase-1, a key enzyme in the regulation of the pathway.

The inhibition of this enzyme stops the whole pathway and the muscle has no available substrate to perform its work. This accounts for the muscular pain (cramps) when the effort is going on and when the muscles are further solicited.

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